The lead brass has been widely used to sanitary hardware, water heating, valves etc. since it has excellent corrosion resistance, cuttability and hot and cold workability. However, because the lead contained in brass tends to dissolve into water and contaminates water source, soil, atmosphere, and so on, the dissolved lead easily has no harmful effect on the human body or other organisms, thus it has become a trend in the art with the development of the lead-free brass substitutes.
The currently widely used environmentally friendly lead-free free-cutting brass alloy for replacing lead brass in Chinese market is the bismuth brass and silicon brass. The cuttability of bismuth brass is approximately close to that of lead brass, but the apparent shortage of bismuth brass is the high sensitivity to stress corrosion due to the high residual stress resulted from growing of bismuth particles during solidification in the alloy. On the other hand, the difficulty of processing parts and components due to bad weldability of lead free bismuth brass is caused by the severe hot brittleness at the temperature between 300° C. and 450° C. (medium temperature). Therefore the reliability of welding joint at the temperature range mentioned above seems to be extremely problematic. At the same time, inefficient cooling condition can easily result in hot cracking during machining metallic parts and components. It is, therefore, difficult to use bismuth brass widely.
As an another substitute for lead brass, the advantages of silicon brass are good hot workability, weldability, dezincification-resistance and stress corrosion resistance, but in comparison with bismuth brass, silicon brass has difficulty in adjusting to high speed cutting lathe because of its shortage of low efficiency of cold processing and short service life of cutters resulted from poor cuttability. Furthermore, the lead-free silicon brass has a high content of copper, generally about between 73 and 77 wt %, even up to between 79 and 83 wt %. Thus, the cost of raw material of silicon brass is much higher than that of bismuth brass.